This is the MXR Smart Gate, model M135, a noise gate with one Trigger Level knob and a switch for three noise ranges: Hiss, Mid and Full. The yellow Gate light comes on when the gate engages.

Hiss works on highs, Mid on mids and Full on lows. Dunlop's manual puts Hiss or Mid on distorted guitar and Full on hum and buzz, like light dimmer noise. It reacts slowly to long, sustained notes and quickly to short ones, and the fast attack keeps the pick attack and overtones. The small button beside the knob is Hi Trigger Range, which stretches the knob's range for very noisy rigs. To quiet a string of pedals, it goes last, just before the amp. Input and the power jack are on the right side, output on the left. It runs on a 9-volt battery under the bottom plate or a 9-volt adapter, and bypass is hardwire.

Silver. Very good condition, shown in the photos. Comes with just the pedal, no box.

Includes: The pedal only, no box